I wouldn't be so quick to dismiss Casio these days. The quality has improved tremendously and I rate it on par with the Yamaha entry level models, if not better.
The cdp-100 is great value for money. i've seen really terrible sets at carrefour but i believe that those are a result of extraordinarily heavy usage at the destructive hands of kids. same goes for the p85 in the yamaha showroom. so you should preferably go to a showroom where u can do a side-by-side comparison of all the models in new condition(which I think you alr might have done that).
sound wise, the yamaha p85 or cdp-100 have no edge over one another. in terms of touch, the cdp-100 packs a slightly heavier weight than the p85. the only reason not to buy the cdp-100 is that the cdp-100 does not have a built-in metronome, however this is not an issue as a metronome can be bought cheaply for little over $20, and is not going to make a significant dent in cost savings of $300+ ($989 for p85+LP5+L85 and $629 for cdp-100).
if there's a reason to buy the p85 over the cdp-100, it would because the p85 full set comes with triple pedals like on a grand piano (soft, sostenuto and sustain) but it is unlikely that as a beginner one would be using anything more than the sustain. the cdp-100 comes with only a crummy sustain pedal-switch; furthermore i dont think the cdp-100 supports half-pedalling. however these are features more for intermediate to advanced pianist.
the sp250 is quite widely shunned because Korg piano sound is not well-liked. however, the onboard speakers of the sp250 really sound splendid and it's more enjoyable to play for long hours compared to the cdp-100 and p85 which are much more tinny and lacking depth. the touch is average, nothing to boast about but nothing to complain about either.
this is my comparison of the three models, based on regular experience playing on all three.
